UBUNTU: [Config] Disable a.out support

UBUNTU: [Config] Disable a.out support

BugLink: https://launchpad.net/bugs/1818552
The a.out core dump handler is broken and will be removed in 5.1 with
upstream commit 08300f4402ab ("a.out: remove core dumping support").
Additionally, all a.out support will be deprecated in 5.1 with upstream
commit eac616557050 ("x86: Deprecate a.out support") and completely
removed in a future release.

Disable it in Ubuntu since it is risky to leave enabled and there are
likely no users that depend on it.

Signed-off-by: Tyler Hicks <tyhicks@canonical.com>
Acked-by: Colin Ian King <colin.king@canonical.com>
Acked-By: You-Sheng Yang <vicamo.yang@canonical.com>
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>